The intravascular placement of a plastics cannula by means of an introducer needle is a common medical procedure in order to administer fluids or drugs into the vascular system, or to sample or monitor blood therefrom. A typical method of utilising such an apparatus is to penetrate the skin and the subcutaneous tissue and thus enter, for example, a vein with a needle carrying a plastics cannula so that both can pass into the vein or the blood vessel. When the needle is withdrawn the plastics cannula is left in the vein and a hub disposed on the cannula at its remote end may then be coupled to an administration set or other suitable apparatus. However, during withdrawal of the needle from cannula blood escapes until the cannula is connected to said administration set or other apparatus.
Blood spillage during needle withdrawal can often be controlled by digital pressure on the skin adjacent the puncture to compress the vein ahead of the cannula tip. Peripheral veins have internal valves therein to prevent backflow of blood, and therefore pressure on the vein ahead of the cannula in the direction of flow of venus blood tends to control blood spillage from the cannula. This technique is effective but occupies both hands of the operator, is not possible with all veins, and requires a high level of competence. This problem has been addressed in our WO88/00842 which provides an intravascular placement apparatus adapted for operative association with an introducer needle; said apparatus comprising,
a cannula provided with a connecter hub at its remote end, and a self-sealing septum disposed across the internal lumen of the cannula whereby the cannula can be positioned with the introducer needle. The use of a self-sealing septum prevents the back flow of blood or other fluids and allows the cannula to be positioned by less skilled staff.
The material from which the septum is formed is usually an elastomeric self-sealing rubber or plastics material. It has been known that a disadvantage of conventional needle tip designs, when utilised for co-operation with such an elastomeric septum is the problem of "coring". Coring occurs when the self-sealing septum material gets held in the needle lumen and either blocks the lumen or becomes discharged into the vascular system of the patient. This problem has been addressed in WO89/06553 (Baxter International Inc). The Baxter disclosure provides a blunt hollow adaptor at the distal end of an extension piece of a vascular placement apparatus so that the hollow adaptor will penetrate a preformed channel in the self-sealing septum and thereby form a channel from the extension piece to the cannula. The blunt hollow adaptor may be coupled directly to an administration set or via an extension piece, so that any change over in the administration set, for example to change one fluid for another, does not entail detachment of the adaptor from the cannula.
The rigid hollow adaptor is preferably formed of a metal or a rigid plastics material. An advantage of this last type of arrangement is that the substantially rigid blunt adaptor prevents needle-stick.
The arrangement of Baxter includes in a first aspect a thin pre-slit septum which may be penetrated by a blunt hollow adaptor. This arrangement is prone to problems in that after use over a number of engagement and disengagement cycles, the pre-slit disc shaped septum does not necessarily close entirely and this allows of the possibility of infection. In the second aspect of the Baxter disclosure there is provided a relatively large blunt hollow adaptor adapted to enter a pre-slit or partially pre-slit septum. The relatively large bore of the blunt adaptor necessarily causes an amount of collateral damage to the septum particularly when the resilient material of the septum has lost some of its resilience through aging.